Recently, in the field of image display apparatus that display images using the electro-optic effects of liquid crystal molecules, there has been proposed a so-called in-plane switching-type (hereafter, IPS-type) image display apparatus that applies an electric field to control the orientation of liquid crystal molecules in a direction parallel to the substrate surfaces that sandwich the liquid crystal layer containing the liquid crystal molecules. Compared to the conventional image display apparatus that applies an electric field in a direction perpendicular to the substrate, the IPS-type image display apparatus has superior characteristics with respect to voltage retention and viewing angle, and therefore, has held special promise in recent years.
In theory, this IPS-type image display apparatus is capable of high-quality display. In actuality, however, fluctuations in the electric potential of signal lines or scanning lines cause disruptions in the electric field that is applied to the liquid crystal layer. Such disruptions are not negligible, and as a result, image quality has not achieved sufficient improvement.
On the other hand, a configuration is known in which the size of the common electrode mounted on the array substrate is enlarged and the signal lines or scanning lines are covered to suppress the influence of electric field components, generated by fluctuations in the electric potential of signal lines or scanning lines, on the liquid crystal layer. For example, as shown in FIG. 12, a configuration comprising scanning line 101, signal line 102, thin film transistor 106 connected to scanning line 101 and signal line 102, pixel electrode 104 connected to signal line 102 via thin film transistor 106, and enlarged common electrode 105 has been proposed.
In the configuration as shown in FIG. 12, common electrode 105 is formed into a lattice shape, widened and arranged so as to cover scanning line 101 and signal line 102. This arrangement enables the electric field components generated by scanning line 101 and signal line 102 to be shielded by common electrode 105.
As another example, an IPS-type image display apparatus having a configuration that completely covers the signal and scanning lines by using a three-dimensionally configured common electrode has been proposed. Specifically, as shown in FIG. 13, by covering signal line 107 with upper electrode 108, lower electrode 109 and contact slit 110, this configuration shields the electric field generated from signal line 107.
As shown in FIG. 13, by adopting a configuration that three-dimensionally covers signal line 107, there is no electric field leakage from signal line 107 to the liquid crystal layer, and degradation of the display image quality is suppressed.
However, as shown in FIGS. 12 and 13, in the case of a configuration in which signal or scanning lines are covered by a common electrode, the aperture ratio may be decreased.
In the case of the configuration shown in FIG. 12, lattice-shaped common electrode 105 must be widened in order to effectively shield the electric field generated from signal line 101 and scanning line 102. In actuality, the electric field generated from signal line 101 and scanning line 102 contains not only components that propagate in a direction perpendicular to the array substrate, but also components that propagate in an oblique direction. Therefore, in order to shield those oblique components, the width of common electrode 105 must be increased. Moreover, it is necessary to allow for errors in positioning of the master pattern during fabrication. Thus, to position common electrode 105 on signal line 101 and scanning line 102, the width of common electrode 105 must be increased further.
In the case of the configuration shown in FIG. 13, it is necessary to additionally enlarge the width of the common electrode, due to the presence of contact slit 110 that is provided in a transverse orientation to signal line 107. In the case where contact slit 110 is arranged in the vicinity of signal line 107, and in the case where signal line 107 and contact slit 110 are arranged in close proximity, the capacitive coupling will influence the voltage fluctuation of signal line 107. Therefore, to lessen the parasitic capacitance generated between signal line 107 and contact slit 110, the configuration must position signal line 107 and contact slit 110 sufficiently far apart. The width of upper common electrode 108 must be enlarged further according to the distance between signal line 107 and contact slit. Even in the configuration shown in FIG. 13, the common electrode will have a large width.
However, generally, in an IPS-type image display apparatus, the electric field generated between a pixel electrode and a common electrode arranged on an array substrate is actually generated between the edge of the pixel electrode and the edge of the common electrode that faces opposite the pixel electrode. Therefore, in the case where the common electrode has a large width, the region that generates the transversely oriented electric field which contributes to the image display becomes narrower, and as a result, the aperture ratio decreases. With the decrease in aperture ratio, the region that contributes to image display becomes smaller in area and, in the image display apparatus configurations shown in FIGS. 12 and 13, brightness of the display image may be reduced.